In a multichannel waveguide device, such as an integrated wavelength dispersive device (for example a planar waveguide microspectrometer) or an optical planar waveguide circuit containing multiple waveguides, there is an increasing demand to connect a large number of waveguides located on a single chip with output readout circuitry. A similar interconnection problem exists when optically coupling a large number of optical input ports, such as VCSELs (vertical cavity surface emitting lasers) or optical fibre arrays to a multichannel optical waveguide device; or when optically coupling together various multichannel waveguide devices.
The optical interconnect problem is discussed for example in the following references, which are incorporated herein by reference: D. A. B. Miller, “Rationale and challenges for optical interconnects to electronic chips,” Proc. IEEE, vol. 88, pp. 728-749 (2000); Y. Li et al., “Optical interconnects for digital systems,” Proc. IEEE, vol. 88, pp. 723-863 (2000).
None of the existing interconnection techniques, electrical or optical, is practical for coupling between a large number, up to tens of thousands or more, of waveguides located on a single chip with input/output device or another optical chip.
Optical off-chip interconnects of up to several hundred channels have been demonstrated for example in optical demultiplexers for WDM applications by using coupling from the chip edge to a fibre array held in a v-groove assembly. However, it is not practical to provide off-chip interconnects of several hundreds or more optical channels using present packaging technology because the alignment tolerances and resulting packaging cost becomes prohibitive. This limitation causes a bottleneck in connecting multichannel waveguide devices with input and output devices or other multichannel waveguide devices.